NIS 2010 Not Recognizing I have Gen Downloader trojans. Help!!

I've been getting a fake popup from Microsoft Windows saying I needed to download an Online Protection Tool.  I scanned twice with NIS 2010 and it didn't find anything wrong.  I scanned again at Microsoft Live Onecare and it didn't find anything either.  I asked on the forums at Microsoft and someone said scan using Stopzilla free version so I did and it found two trojans named gen downloader.  It won't remove them until I pay for the program.  I think NIS should have found them and can anyone tell me how to get rid of them using my Norton service which I paid for??  Thanks for any help!